The control region of the human adenovirus genome and its relation to the E1A gene has been extensively studied. It is known that the protein products of the adenovirus E1A gene may act as positive and negative regulators of early viral gene expression, and that E1A products regulate at the transcriptional level. Sequences located 5' to the early viral regions contain sites which confer regulation by the E1A gene product, Weeks and Jones (1983). Positive and negative autoregulation of the adenovirus E1A gene transcription by E1A gene products has been reported. Tibbetts et al. (1986).
The E1A control region and E1A gene expression for adenovirus type 3 (Ad3) was further studied by Larsen, et al. (1986). They reported a defective mutant of Ad3, designated Ad 3 hr 15, which failed to propagate on normally permissive A549 cells, but had greater infectivity than wild-type Ad3 in the adenovirus type 5 (Ad5) DNA-transformed 293 cells. Investigation of the genomic alteration revealed that the Ad 3 hr 15 mutant had two short tandem duplications of viral DNA sequences near its left end, 5' to the E1A gene. Marker rescue experiments with plasmid-cloned left end DNA sequences of Ad3 indicated that the duplications 5' to E1A were responsible for the Ad 3 h 15 defect, and the E1A gene of the variant was functional. The E1A gene promoter with the reiterated sequence provides a transcriptional control element adapted for regulation of gene expression in animal cells, as described in the co-pending application of Tibbetts et al., Ser. No. 897,042, filed Aug. 15, 1986, now patent 4,775,630.
As described by Larsen et al. (1986) and in the cited co-pending application, the Ad3 hr15 promoter for the E1A gene responds in trans to Ad3 E1A wild-type products to repress the expression of the E1A gene or other gene under its control. The response to adenovirus type 5 (Ad5) E1A wild-type gene products enhances expression of the controlled gene.
Since the duplicated sequence of this promoter makes it highly sensitive to both positive and negative effects of E1A gene products, it is important to regulate the promoter. Prior to the present invention, it was not known how to produce Ad3 E1A gene products which have a net stimulatory action on the Ad 3 h 15 promoter.